There is increasing interest in exploring the potential therapeutic uses of adult stem cells from bone marrow. Currently, however, it is not understood which stem cell populations or cellular phenotypes are best suited to effectively treat a variety of diseases that may be amenable to such a therapeutic approach. There is very little fundamental information on the basic biology of adult bone marrow stem cells and whether or not they will provide a source of cells that can repair damaged tissues and ameliorate a disease process. Thus, we have proposed a series of experiments to test the central hypothesis that purified sub-populations of adult rat bone marrow-derived stem cells are effective in repairing injured cardiac and pulmonary tissues. Three specific aims have been developed to directly test the hypothesis: Specific Aim: 1. To establish the morphologic and molecular profiles of purified adult stem cell sub-populations from the bone marrow of male transgenic rats that ubiquitously express green fluorescent protein (GFP). 2. To determine the differentiation potential of the stem cell sub-populations in ex vivo co-culture assays we have recently developed with normal and injured primary cells from cardiac and pulmonary tissues. 3. To determine the engraftment and differentiation potential of the stem cell sub-populations in a rat model of monocrotaline-induced pulmonary hypertension.